Magnetoresistive (MR) technology can be utilized in a variety of commercial, consumer, and industrial detection applications. Anisotropic Magnetoresistance (AMR) is the property of a material in which the electrical resistance can change depending on the angle between the direction of electrical current and orientation of magnetic field is observed. AMR array position sensors yield a very accurate signal with respect to the position of a magnet. In conventional MR systems, for example, a device may be provided for determining the position of a member movable along a path. The device includes a magnet attached to the movable member and an array of AMR sensors located adjacent the path. As the magnet approaches, passes, and moves away from a sensor, the sensor provides a varying output signal, which can be represented by a single characteristic curve that is representative of any of the sensors.
To determine the position of the movable member, the sensors can be electronically scanned and data selected from a group of sensors having an output that indicates the relative proximity to the magnet. A curve-fitting algorithm can then be utilized to determine a best fit of the data to the characteristic curve. The position of the magnet and therefore the movable member may be determined by placing the characteristic curve along a position axis.
FIGS. 1A and 1B illustrates a prior art AMR position sensing system 100. The AMR position sensing system 100 generally includes a magnet 110 and an array of AMR position sensors 130 to sense the relative position of the magnet 110 within the array of AMR position sensors 130. The magnet 110 must be positioned such that the magnetic flux lines as indicated by arrow 120 of the magnet 110 are in the same plane of the AMR position sensors 130. The magnet 110 generates magnetic flux lines 120 while moving in the direction as indicated by arrow 140. If the air gap 160, the distance between the magnet 110 and the AMR position sensors 130, is changed significantly after calibration, the performance of the AMR position sensors 130 also changes. FIG. 1B illustrates the magnetic flux lines 120 in different direction when the magnet moves in the same plane of the AMR position sensors 130 in the direction as indicated by arrow 140.
FIG. 2 illustrates two AMR bridge signals 200 and 210 obtained from the prior art AMR position sensing system 100 as the magnet 110 moves and passes the AMR position sensors 130. The bridge signals 200 and 210 can be generated as the magnet 110 moves and passes through the AMR position sensors 130. The peaks 220 and 230 correspond to the position when the magnetic flux lines 120 are perpendicular to half the AMR sensor runners 135 and parallel to the others in the AMR position sensors 130. The position at which the magnetic flux lines 120 are parallel or perpendicular to the AMR sensor runners 135 changes with respect to the changes in the air gap 160, which in turn changes the bridge signal 200 generated from the AMR position sensors 130 respect of position. The problem associated with such prior art position sensing system 100 is that as the distance between the AMR position sensors 130 and the magnet 110 changes, the signal changes decreasing repeatability of the sensor. Hence, the overall performance of the AMR position sensors decreases.
Based on the foregoing, it is believed that a need exists for an improved AMR array magnetic design for improved sensor flexibility and improved air gap performance as described in greater detail herein.